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Although Stihl chain-saw chains are pre-stretched by the factory, the chains heat up and stretch slightly during normal cutting operations; consequently re-tensioning is required from time to time while working to prevent unnecessary wear to the sprocket and chain bar. In addition, link rivets eventually wear, causing further stretching. Depending on the model, there are two ways of tensioning Stihl chains. Some require tools, and some can be adjusted by hand.

Preparation

Before starting work, check the underside of the chain bar. If the chain sags and there’s a gap between the chain and the bar, adjust the tension. Loosen the two nuts securing the sprocket cover and locate the tension adjusting screw. On some models it’s visible through a hole in the sprocket cover between the two studs; on others, it’s situated in the sprocket housing behind the cutting bar. Turn the screw clockwise until the chain settles flush against the groove in the chain bar, then pull the chain down to check its tension. A properly adjusted chain should move slightly and reveal three to five link sliders between the chain and the bottom of the chain bar. Finally, tighten the nuts and slide the upper part of the chain backward toward the chain saw. It should move freely without resistance.

Running Adjustment

Every hour or so, stop the chain-saw’s engine and carry out the above procedure to take up the slack caused by the heated chain expanding. After work, turn the engine off, undo the two sprocket cover nuts, and loosen the chain tension screw a full turn counterclockwise before tightening the nuts. This prevents the chain from binding on the chain bar and stressing the chain sprocket as it cools down and shrinks. This precaution is especially important during frosty weather.

Quick Chain Tensioner

Some Stihl chain saws are equipped with a Quick Chain Tensioner that allows adjustment without using tools. These saws are fitted with a large wingnut on the sprocket cover in lieu of the two studs In addition, instead of a chain-tensioning screw, there’s an adjusting wheel on top of the sprocket cover you can rotate by hand. To loosen the chain bar, flip up the half-moon-shaped wingnut handle upright, grip the handle and rotate the wingnut half a turn counterclockwise. Once the bar is loose, turn the adjusting wheel clockwise to increase chain tension, and counterclockwise to reduce tension, then tighten the wingnut and check for correct chain tension.

Safety Precautions

Always shut off the engine before attempting field adjustment. Even though the centrifugal clutch prevents the chain from moving while the engine is idling, a worn clutch could cause the chain to move suddenly while you’re working. Before replacing a worn chain, use a small screwdriver to clean out any compacted dirt inside the chain bar slot. This prevents the chain from jumping out of the slot during operation. In addition, any compacted grit and sawdust left inside the slot soaks up chain lubricant and causes unnecessary wear. Never slide the upper portion of the chain away from the machine while checking to see that it moves freely after adjustment. Always slide the upper part of the chain toward the chain saw to keep the forward-facing cutting edges from contacting your hand.Always wear eye protection and heavy working gloves while operating or adjusting a chain saw.

About the Author

After graduating from the University of the Witwatersrand and qualifying as an aircraft engineer, Ian Kelly joined a Kitchen remodeling company and qualified as a Certified Kitchen Designer (CKD). Kelly then established an organization specializing in home improvement, including repair and maintenance of household appliances, garden equipment and lawn mowers.